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  1. #1
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    Default Too *Much* Crankcase (PCV) Vacuum?

    While the dealer was performing the air bag recall service I asked that they check the PCV breather vacuum.

    The tech reported that vacuum was too high and suggested that may be due to plugged passages to the oil pan. In 18 years on this forum, I don't recall anyone else ever mentioning the crankcase vacuum being too high. The diagnostic indication mentioned for a clogged PCV has always been too little vacuum.

    So, I'd appreciate feedback from you experienced members who understand this PCV breather system better than I do.

    There are only 85,000 miles on this car. PCV system has never been serviced. 45% highway and 55% around town mileage, so short trips may have played a role, though we do our best to combine errands and get the engine fully warmed up on each outing. Ran Valvoline semi-synthetic blend oil for the first 40,000 miles, and Mobil 1 Euro 0W40 since. Oil changes annually, so typically 3,000 - 5,000 miles.
    Last edited by Pennhaven; 03-16-2022 at 10:25 AM. Reason: Added oil change interval.
    '04 XC70, Ash Gold / Taupe, Premium, Touring, Tinted Rear Glass, Rear Skyddsplåt, Wing Profile Load Bars, USA Spec 11,
    StonGard Light Protection, Yokohama YK740 GTXs, Meyle HD Sway Bar Links, ipd HD TCV, subframe & top brace poly bushing inserts,
    TitaniumTim XC Cup-holder Coasters.

  2. #2
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    Quote Originally Posted by Pennhaven View Post
    While the dealer was performing the air bag recall service I asked that they check the PCV breather vacuum.

    The tech reported that vacuum was too high and suggested that may be due to plugged passages to the oil pan. In 18 years on this forum, I don't recall anyone else ever mentioning the crankcase vacuum being too high. The diagnostic indication mentioned for a clogged PCV has always been too little vacuum.

    So, I'd appreciate feedback from you experienced members who understand this PCV breather system better than I do.

    There are only 85,000 miles on this car. PCV system has never been serviced. 45% highway and 55% around town mileage, so short trips may have played a role, though we do our best to combine errands and get the engine fully warmed up on each outing. Ran Valvoline semi-synthetic blend oil for the first 40,000 miles, and Mobil 1 Euro 0W40 since. Oil changes annually, so typically 3,000 - 5,000 miles.
    Since I can attach a photo follow this link to see a good diagram of the PCV system.

    https://www.matthewsvolvosite.com/fo...ic.php?t=60728


    With this PCV system there are two sources of vacuum because of the turbo and whether the intake manifold is under boost pressure or not. At idle and low load with no boost the intake manifold vacuum provides crankcase vacuum through a small hose from the banjo bolt on the manifold that's goes to a hose just above the oil trap. Under boost conditions when the manifold is under pressure the vacuum comes from a larger PCV hose that is routed to the air intake hose are just before the turbo. This is also an area where there's a heating element, PTC. When the turbo is spooled up there's vacuum created within the intake tube just before the turbo and this provides crankcase vacuum for the PCV system because there's no intake manifold vacuum available.

    Did the tech say when there was too much vacuum? At idle or higher loads with turbo pressure at the manifold?
    Did they measure how much vacuum there is and what is considered too much? The small diameter (3mm ID) vacuum hose from the manifold to the PCV system is a designed in restricted path to meter air so I wouldn't suspect this path to even be able of providing too much vacuum but I don't know for certain. The other vacuum source from the air intake tube when there's turbo boost is more of a question, I just don't know how much vacuum is produced from this source or how it's regulated or even if it's regulated. There's obviously nothing clogged up from the vacuum sources to the crankcase depending on the vacuum under the different conditions. It would help to know if there's too much vacuum during idle/low load conditions or boosted conditions or both.

  3. #3
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    No, I didn't actually speak with the tech, only the service advisor, and no mention as to actual vacuum reading or whether at idle or under boost, only this note: "BREATHER SUCKING TO (sic) MUCH VACUUM POSSIBLE OIL PASSAGES PLUGGED GOING TO OIL PAN"

    Service advisor did not press me to have breather service performed. If service is necessary I'll likely either do it myself or have and independent shop do it. Now I'm trying to determine if it is actually even necessary at this point,. i.e., What blockage would actually cause "too much" vacuum.
    '04 XC70, Ash Gold / Taupe, Premium, Touring, Tinted Rear Glass, Rear Skyddsplåt, Wing Profile Load Bars, USA Spec 11,
    StonGard Light Protection, Yokohama YK740 GTXs, Meyle HD Sway Bar Links, ipd HD TCV, subframe & top brace poly bushing inserts,
    TitaniumTim XC Cup-holder Coasters.

  4. #4
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    Quote Originally Posted by Pennhaven View Post
    No, I didn't actually speak with the tech, only the service advisor, and no mention as to actual vacuum reading or whether at idle or under boost, only this note: "BREATHER SUCKING TO (sic) MUCH VACUUM POSSIBLE OIL PASSAGES PLUGGED GOING TO OIL PAN"

    Service advisor did not press me to have breather service performed. If service is necessary I'll likely either do it myself or have and independent shop do it. Now I'm trying to determine if it is actually even necessary at this point,. i.e., What blockage would actually cause "too much" vacuum.
    I can't see how the passage to the oil sump would create too much vacuum in the crankcase even if blocked. I think this is just speculation by a tech that doesn't understand the PCV system very well. I was trying to think what could possibly cause too much vacuum and this assumes there really is too much vacuum and all I can think of are real long shots. Any work done on the car recently?

    Did you have any problem with the car when you asked them to check the PCV system/vacuum or was it just a routine check you wanted them to do?

  5. #5
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    You could remove the oil filler cap, put a plastic glove over the opening, then start the car and see if the glove inflates, a sure sign that your PCV has blockage. This I think might be referred to as "negative vacuum". Could this be what the tech meant when he said "too much vacuum"?

    Maybe you need to ask the tech what test/procedure he used to measure the vacuum.
    2007 XC70, 206,000 miles
    2002 V70XC, 130,000 miles, parts car

  6. #6
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    Quote Originally Posted by FirstVolvo View Post
    I can't see how the passage to the oil sump would create too much vacuum in the crankcase even if blocked. I think this is just speculation by a tech that doesn't understand the PCV system very well. I was trying to think what could possibly cause too much vacuum and this assumes there really is too much vacuum and all I can think of are real long shots. Any work done on the car recently?

    Did you have any problem with the car when you asked them to check the PCV system/vacuum or was it just a routine check you wanted them to do?
    No, no problem with the car and no recent work done. I do the glove test at every oil change and there is good vacuum at the oil filler cap at idle. The only reasons I had them check it is the accumulated short trip mileage and because I don't know how to test the boost circuit myself.

    I'm inclined to agree with you, that the tech may not know enough. I couldn't figure how there would be too much vacuum either. Which is why I'm asking here. Unless someone with experience here has a good theory, I'm may be inclined to let it go.
    '04 XC70, Ash Gold / Taupe, Premium, Touring, Tinted Rear Glass, Rear Skyddsplåt, Wing Profile Load Bars, USA Spec 11,
    StonGard Light Protection, Yokohama YK740 GTXs, Meyle HD Sway Bar Links, ipd HD TCV, subframe & top brace poly bushing inserts,
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  7. #7
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    Quote Originally Posted by Pennhaven View Post
    No, no problem with the car and no recent work done. I do the glove test at every oil change and there is good vacuum at the oil filler cap at idle. The only reasons I had them check it is the accumulated short trip mileage and because I don't know how to test the boost circuit myself.

    I'm inclined to agree with you, that the tech may not know enough. I couldn't figure how there would be too much vacuum either. Which is why I'm asking here. Unless someone with experience here has a good theory, I'm may be inclined to let it go.

    One theory I have is the PTC nipple could be clogged and this may allow too much vacuum to build up during idle or low loads. The PTC is located in the air intake tube down near the inlet of the turbo. The PTC is an open fixed orifice size opening with a heating element that meters the amount of air through it. If it is clogged you would have a problem with crankcase pressure becoming too high during higher throttle loads and under turbo boost conditions. This is why I asked if there was too much vacuum under this condition too. I would think you might be able to detect this with the glove test at idle were the glove would be suck down faster and harder or more than expected although this could be subjective. With my car there is a slight crankcase vacuum at idle and the glove does such down but you can tell it's not much vacuum.
    The hose with the PTC inline comes off the top of the oil trap and goes to the air intake tube before the turbo and this would regulate or limit crankcase vacuum during idle/low loads because there no vacuum and a source air flow but if clogged maybe this would allow too much vacuum to build up. Just a theory and this could be completely wrong but you could check the PTC opening by pulling of the hose to the PTC and inspecting. I can't recall if you have to pull the turbo to air filter box intake tube out too to inspect the PTC because of the viewing angle so you might off to do this too.

  8. #8
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    Quote Originally Posted by FirstVolvo View Post
    One theory I have is the PTC nipple could be clogged and this may allow too much vacuum to build up during idle or low loads. The PTC is located in the air intake tube down near the inlet of the turbo. The PTC is an open fixed orifice size opening with a heating element that meters the amount of air through it. If it is clogged you would have a problem with crankcase pressure becoming too high during higher throttle loads and under turbo boost conditions. This is why I asked if there was too much vacuum under this condition too. I would think you might be able to detect this with the glove test at idle were the glove would be suck down faster and harder or more than expected although this could be subjective. With my car there is a slight crankcase vacuum at idle and the glove does such down but you can tell it's not much vacuum.
    The hose with the PTC inline comes off the top of the oil trap and goes to the air intake tube before the turbo and this would regulate or limit crankcase vacuum during idle/low loads because there no vacuum and a source air flow but if clogged maybe this would allow too much vacuum to build up. Just a theory and this could be completely wrong but you could check the PTC opening by pulling of the hose to the PTC and inspecting. I can't recall if you have to pull the turbo to air filter box intake tube out too to inspect the PTC because of the viewing angle so you might off to do this too.
    Thanks. Sounds reasonable. At least worth a look. Maybe in a day or two.
    '04 XC70, Ash Gold / Taupe, Premium, Touring, Tinted Rear Glass, Rear Skyddsplåt, Wing Profile Load Bars, USA Spec 11,
    StonGard Light Protection, Yokohama YK740 GTXs, Meyle HD Sway Bar Links, ipd HD TCV, subframe & top brace poly bushing inserts,
    TitaniumTim XC Cup-holder Coasters.

  9. #9
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    I was able to get my bore scope into the neck of the PTC nipple without too much disassembly. (Good thing because I couldn't even get the intake tube to release from the filter box cover. If there is an easy trick, I'd love to hear it.)

    The PTC looks pretty darn clean to me, unless I don't know what to look for. https://photos.app.goo.gl/9GrE69ptzh8opeWA7

    Any opinions? Should I shoot some brake cleaner down there while the hose is off?

    I also did a glove test at the oil filler at idle, and the dealer tech appears to be correct. It seems to me that there is noticeably more suction than in the past. It pulls the glove down at least a quarter inch. Where if my memory is correct, as FirstVolvo noted, earlier it just barely pulled it down.
    Last edited by Pennhaven; 03-21-2022 at 12:11 PM. Reason: typo: I meant oil "filler"
    '04 XC70, Ash Gold / Taupe, Premium, Touring, Tinted Rear Glass, Rear Skyddsplåt, Wing Profile Load Bars, USA Spec 11,
    StonGard Light Protection, Yokohama YK740 GTXs, Meyle HD Sway Bar Links, ipd HD TCV, subframe & top brace poly bushing inserts,
    TitaniumTim XC Cup-holder Coasters.

  10. #10
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    I did some more searching, with different terms, and found a thread at Swedespeed that discusses high crankcase vacuum. https://www.swedespeed.com/threads/c...1/post-2673465

    The assertion there is that high vacuum is caused by a clogged long PCV tube. I also found a video at FCP, https://www.fcpeuro.com/products/vol...s60turbopcvkit , showing how the entire tube does not have to be replaced, as they have a partial banjo-bolt tube, that for less money and effort can replace just the portion where the blockage occurs. Not sure whether I'll DIY this route, with just a new trap and partial hose, or have an indy shop do it whichever way they suggest. I'm getting on in years, and not sure I want to tackle the job myself what with the removal of the intake manifold and fuel rail.

    Posting this for others' info, but still looking for advice / confirmation from anyone who knows better!
    '04 XC70, Ash Gold / Taupe, Premium, Touring, Tinted Rear Glass, Rear Skyddsplåt, Wing Profile Load Bars, USA Spec 11,
    StonGard Light Protection, Yokohama YK740 GTXs, Meyle HD Sway Bar Links, ipd HD TCV, subframe & top brace poly bushing inserts,
    TitaniumTim XC Cup-holder Coasters.

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